JPH05130542A - Digital video signal control circuit - Google Patents

Abstract

PURPOSE:To perform the white level balance adjustment, cut-off adjustment, and saw tooth wave modulation in a digital part without preventing the correction in the video signal processing circuit correcting the inter-channel deviation of a video signal divided into the plurality of channels with the use of a reference signal. CONSTITUTION:A multiplier 29 multiplies a video signal represented by the 8-bit digital signal where the white and black levels are adjusted within the range of the prescribed digital value by a coefficient (k) given from a white level balance coefficient ROM 35 according to the data of a white level balance changeover switch 38, thereby switching the white level. The saw tooth modulation is performed by multiplying the video signal by a coefficient (n) given from a saw tooth wave inclined changeover switch 39 and the counter 40 of the horizontal pulse. It is added to a coefficient (c) given from a cut-off adjustment switch 42, thereby changing the cut-off level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital video signal control circuit, and more particularly to a digital video signal control circuit applicable to a projection type liquid crystal display device.

[0002]

2. Description of the Related Art In a device for correcting deviation between video signal channels of multi-divided video signals, a reference signal having the same potential as a potential corresponding to a black level and a white level of an input video signal is a vertical retrace line of the video signal. Inserted in the period. It is conceivable that the reference signal is taken in by the output section of each of the channels which are multi-divided and the potential thereof is fed back by digital data so as to eliminate the deviation between the channels.

[0003]

In the projection type liquid crystal display device to which the present invention is applied, the following problems occur when the light source incident on the liquid crystal panel is uniform when it is mass-produced. Can happen.

FIG. 4 shows the applied voltage (X
FIG. 6 is a diagram showing the relationship between the (axis) and the amount T% (Y axis) of light passing through the liquid crystal at that time for each color R, G, B of transmitted light. Figure 4
, R, G, and B have different light transmission rates depending on the applied voltage, and are regarded as white (applied voltage with the largest amount of light transmission) and black according to each color. The level (applied voltage with the least amount of light transmission) varies. Therefore, when mass-producing liquid crystal panels, it is necessary to adjust the transmittance of each color for each panel.

Further, in an image projected by using a liquid crystal projection device, a difference in brightness occurs at the upper and lower parts of the screen even if an applied voltage of the same black level is applied (due to the incident angle of light on the liquid crystal panel). Under these conditions, it is necessary to optimally express white and black on the entire screen when the transmitted lights of the three liquid crystal panels are combined in the projection type liquid crystal display device.

These phenomena mainly occur due to liquid crystal material characteristics, alignment film material and electrical characteristics, orientation angle, etc., but it is necessary to adjust each liquid crystal panel so as to obtain an optimum hue.

In the above-mentioned video signal inter-channel deviation correction apparatus, video signal cut-off adjustment (obtaining an optimum black level), white balance adjustment (obtaining an optimum white level), sawtooth wave modulation ( Adjustments (to compensate for the black level disparity between the top and bottom of the screen) must be made in an analog fashion outside the feedback loop, which again causes channel-to-channel deviations and can make the display screen unsightly. Further, if these adjustments are made in the analog portion of the input section, it is necessary to make the full scale range of the AD converter large, resulting in a reduction in resolution.

The present invention has been made in order to solve the above problems, and in an image signal channel deviation correcting device applied to a projection type liquid crystal display device, an image signal is accurately and effectively cut. Off adjustment, white balance adjustment, and sawtooth wave modulation.

[0009]

SUMMARY OF THE INVENTION A digital video signal control circuit according to the present invention comprises a means for multiplying an input digital video signal by a white balance coefficient determined by a white balance changeover switch, and a bit of the multiplied digital video signal. Inverting means, means for adding inversion correction data determined by the white balance changeover switch to the inverted digital video signal, and multiplication of the added digital video signal by a sawtooth wave coefficient determined by the sawtooth wave changeover switch and the horizontal line counter. Means and
A means for adding the reference black level data determined by the white balance changeover switch to the multiplied digital video signal, and a means for adding the cutoff data determined by the cutoff adjustment switch to the added digital video signal.

[0010]

According to the present invention, white balance adjustment, cutoff adjustment, and sawtooth wave modulation are performed in a feedback loop for correcting deviation between channels of a video signal divided into multiple channels.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

In this embodiment, in a video signal processing circuit for a high-definition liquid crystal projector, a video signal for correcting inter-channel deviation of a video signal divided into multiple channels within a vertical blanking period of a high-definition television signal. In the processing method, the white balance adjustment, the cutoff adjustment, and the sawtooth wave modulation for correcting the black level difference between the upper and lower screens of the projection type liquid crystal display device are performed in the processing method.

Before describing the present embodiment, a video signal processing method for channel deviation correction will be briefly described with reference to FIG. FIG. 1 is a diagram showing the configuration of an inter-channel deviation correction device for multi-divided video signals.

Here, the processing of the R signal will be described, but the same applies to the G signal and the B signal.

During the blanking period of the input video signal, the changeover switch 4 is connected to the side b, and the reference signals corresponding to the black level and the white level of the video signal generated by the reference signal generator 20 are processed.

In the AD converter 6, the binary reference signal is set so as to fill the full-scale range, and the resolution is set as high as possible. Next, the video signal portion passes through the gamma circuit 7, and the video signal control circuit 28
And the reference signal portion is divided into multiple channels through the gamma through circuit 8 and converted into analog signals by the DA converters 9 _1-n in each channel.

The DA converter 9 _1-n has an inversion function and inverts the signal, for example, every horizontal period. Then, the adder 11 _1-n is used for each of the normal rotation and the reverse rotation.
At, an offset potential is applied and signal processing for AC driving of the liquid crystal is performed.

After that, by opening / closing the switches 18 _1-n , the black level and the white level of the reference signals of the respective signals are taken out and taken into the microcomputer 21 as a digital value by the AD converter 23. Based on this data, the microcomputer 21 determines the correction DA converters 10 _1-n , 25
_The data sent to each of _1-n , 13 _1-n , and 14 _1-n are adjusted to finally obtain a suitable multi-channel divided video signal having no level deviation from the output of R _1-n .

FIG. 2 shows a video signal control circuit 2 according to the present invention.
It is a block diagram which shows the principal part of 8. Referring to FIG. 2, the video signal control circuit adjusts the white balance when the respective colors of R, G, and B are combined, and adjusts the optimum value of the black level. The purpose is to correct the black level difference between the upper and lower parts of the screen. This embodiment will be described below with reference to FIG.

FIG. 3 is a diagram showing waveforms of video signals in the respective parts shown in FIG. The video signal output from the gamma circuit 7 is an 8-bit digital signal, and its white level and black level are digital values FFH, 00, respectively.
It is adjusted so that it becomes H (see the waveform diagram of FIG. 3, but a ramp wave is used as an example).

In the multiplier 29, the white balance coefficient k according to the data of the white balance changeover switch 38 is given as a digital value from the white balance coefficient ROM 35, the video signal is multiplied by k, and the white level is changed. .. (See Figure 3). The output signal is 9-bit data.

Next, the inversion circuit 34 inverts the bit of the signal data (see FIG. 3). In the adder 30, the inversion correction data a is given from the inversion correction ROM 36 according to the white balance changeover switch so that the white level of the inverted video signal becomes the digital value 00H, and the addition of the signal data and -a is performed ( (See FIG. 3).

The multiplier 31 corrects the black level difference (black floating, black sinking) between the upper and lower parts of the screen, which is a problem for the projection type liquid crystal display device, so that the white level is fixed and the black level is changed between the upper part and the lower part of the screen. The sawtooth wave coefficient n (n is 1 in the horizontal line at the center of the screen) for the above is given by the sawtooth wave inclination ROM 41 by the data determined by the sawtooth wave inclination changeover switch 39 and the counter 40 based on the horizontal pulse, and is multiplied by the signal data. (See Figure 3).

In the adder 32, the reference black level setting ROM is set according to the data of the white balance changeover switch 38.
The reference black level data b is given from 37, and the signal data and b are added (see FIG. 3). this is,
This is performed to correct the change in black level when white balance adjustment is performed. In the adder 33,
In order to optimize the black level of the screen, the cut office data c from the cutoff adjustment switch 42 is added (see FIG. 3).

The digital video signal thus obtained is divided into channels and DA-converted. The white balance coefficient k should be set with a center value of 1, the sawtooth wave tilt coefficient n should be 1 at the center of the screen, and the addition / subtraction constants a, b, c.
For, it is necessary to set so as not to exceed the 9-bit full scale range.

As for the order of adjustment, with the white balance coefficient k = 1 and the sawtooth wave inclination coefficient n = 1 (inclination is 0), the cutoff adjustment is performed so that the horizontal line at the center of the screen has the optimum black level. Adjust the switch 42. Next, with the sawtooth wave inclination changeover switch 39. Adjust the black level at the top and bottom of the screen. Finally, the white balance is adjusted by the white balance changeover switch 38.

Regarding the reference signal portion,
After passing through the gamma through circuit 8, the video signal control circuit 28
Since channel division and DA conversion are performed without passing through, the reference value (data to be compared with the reference signal) in the microcomputer is set even if the white level and the black level of the video signal change due to white balance or cutoff adjustment. No need to change.

The digital resolution in this embodiment is not particularly specified and is merely an example.

[0029]

As described above, according to the present invention, white balance adjustment is performed in a feedback loop for correcting inter-channel level deviation of multi-channel divided video signals.
Cutoff adjustment and sawtooth wave modulation are performed by digital processes. As a result, in the projection type liquid crystal display device, it is possible to provide a digital video signal control circuit capable of accurately and effectively adjusting the cutoff of the video signal, the white balance adjustment, and the sawtooth wave modulation.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus for correcting deviation between video signal channels of a multi-divided video signal including a digital video signal control circuit of the present invention.

FIG. 2 is a block diagram showing a digital video signal control circuit.

FIG. 3 is a diagram showing signal waveforms at various parts of the components shown in FIG.

FIG. 4 is a diagram showing the relationship between the applied voltage and the amount of light transmitted through the liquid crystal in a normally white liquid crystal panel.

[Explanation of symbols]

 7 Gamma circuit 28 Video signal control circuit 29, 31 Multiplier 30, 32, 33 Adder 35 White balance coefficient ROM 36 Inversion correction ROM 37 Reference black level setting ROM 38 White balance changeover switch

Claims (1)

[Claims] 1. A means for multiplying an input digital video signal by a white balance coefficient determined by a white balance changeover switch, a means for inverting the bit of the multiplied digital video signal, and a white balance for the inverted digital video signal. Means for adding inversion correction data determined by a changeover switch, means for multiplying the added digital video signal by a sawtooth wave coefficient determined by a sawtooth wave changeover switch and a horizontal line counter, and the multiplied digital video signal to the white A digital video signal control circuit comprising: means for adding reference black level data determined by a balance changeover switch; and means for adding cutoff data determined by a cutoff adjustment switch to the added digital video signal.